McKenzie has appeared in the first and third films in Peter Jackson's Lord of the Rings trilogy. His silent role in the first film as Figwit achieved some minor internet fame, which led to Jackson giving him a line in the third film. In April 2011, McKenzie was cast as the elf Lindir for The Hobbit. His father Peter McKenzie played the role of Elendil in Lord of the Rings.

Along with Clement, McKenzie was featured as one of 2008's "100 Sexiest People" in a special edition of the Australian magazine Who.

He is married to New Zealand publicist Hannah Clarke[7][8] and currently maintains residences in Los Angeles, New York City and Wellington, New Zealand. They have two children; daughter Vita, born in 2009 and son Leo, born in 2011.[9]